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Thread: inadequate overhead voltage?

  1. #31

    Default Re: inadequate overhead voltage?

    Quote Originally Posted by mercrazy View Post
    boards get humiseal so that's out. blowing open is ok because i have proof of electrical damage and light may still work. blowing shorted causes blown fuses and light is unusable. wish i knew which way it blows. i may layout the board with reset fuse only to TVS.
    i was concerned about fuse resistance reducing effectiveness of TVS. i could place jumper instead of fuse if need be.
    i've been using smaj24, 26, and 33 for years without a fuse and haven't seen but one damaged board. this guy had major stator/voltage regulator failure and fire which no TVS could stop. so maybe i'm worrying too much.
    for RDSon, i'm trying to save every last bit of voltage i can. i'm pulling 800mA and a schottky was dropping 400mV. this only gave me about 200mV extra overhead depending on LED Vf variance. i'm trying to have close to 1 volt extra overhead to compensate for bad connections, switches, etc.
    you guys are up too late and too early like me. i'm old is my excuse.
    thanks again
    Typical fail is a short which is what you want as it takes out the fuse and protects the equipment. If the TVS fails short then it is user error.

    What is the resistance of your inductor? May be better off getting better LED bins.

  2. #32

    Default Re: inadequate overhead voltage?

    i try to stay below 200mOhms on inductors.
    i don't have a choice on LED bins, that's why i'm going to all this trouble.

  3. #33

    Default Re: inadequate overhead voltage?


  4. #34
    Flashaholic* DIWdiver's Avatar
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    Default Re: inadequate overhead voltage?

    I don't see any reason that shouldn't work. You lose some efficiency and overhead voltage switching the FET reverse polarity protection to diode. In this application I think that's not a problem, so schottky diodes are probably better than the FET solution; cheaper, smaller, and work a bit better, though the latter is probably insignificant.

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